Searches for Massive Highly Ionising Particles at the ATLAS Experiment and in Polar Volcanic Rocks, and Performance Studies of the First Level ATLAS Trigger System Katarina Bendtz Doctoral Thesis in Physics Department of Physics Stockholm University Stockholm 2016 ii Doctoral Thesis in Physics Searches for Massive Highly Ionising Particles at the ATLAS Experiment and in Polar Volcanic Rocks, and Performance Studies of the First Level ATLAS Trigger System Katarina Bendtz Department of Physics Stockholm University Roslagstullsbacken 21 Stockholm, Sweden 2016 ISBN 978-91-7649-293-2 c Katarina Bendtz, 2016 Printed by Holmbergs, Malm¨o,Sweden, 2016. Cover illustration by Julia Eriksson Abstract The Standard Model (SM) of particle physics describes the elementary particles and their interactions. Despite passing a number of high preci- sion falsification tests, it is nevertheless argued that the SM suffers from a number of shortcomings. Many Beyond the Standard Model (BSM) theories have therefore been postulated. Exotic highly ionising particles such as magnetic monopoles and Highly Electrically Charged Objects (HECOs), with masses at or above the TeV-scale, are predicted in many of these theories. Monopoles arise naturally in grand unification theories. Proposed candidates for HECOs are Q-balls, strangelets and micro-black hole remnants. The Large Hadron Collider (LHC) at CERN is the world's largest and most powerful particle accelerator, colliding protons at centre-of-mass en- ergies up to 13 TeV. One of the main purposes of the LHC is to search for particles beyond the SM. The research presented in this thesis comprises a search for magnetic monopoles and HECOs at one of the largest of the LHC detectors, the ATLAS detector. In addition, studies were made on the performance of the ATLAS trigger system, which is responsible for making the initial online selection of interesting proton-proton events. The search for monopoles and HECOs at ATLAS was conducted us- ing a customized trigger and selection variables optimized for the non- standard particle signature in ATLAS. The dataset corresponds to an in- tegrated luminosity of 7.0 fb−1 and the centre-of-mass energy was 8 TeV. No events were observed and upper limits on production cross-sections were set for monopoles and HECOs of masses 200-2500 GeV and charges in the range 0:5 2:0 gD, where gD is the Dirac charge, and 10 60 e, − − respectively. Magnetic monopoles were also sought in polar volcanic rock using a SQUID magnetometer at ETH, Z¨urich. No candidates were found leading to limits on the monopole density in polar igneous rocks of 9:8 10−5=gram. · iii iv This thesis is dedicated to everyone. v vi Publications Included in the Thesis The following papers, referred to in the text by their Roman numerals, are included in this thesis. Paper I ATLAS Collaboration. The ATLAS transverse-momentum trigger performance at the LHC in 2011, ATLAS-CONF-2014-002 CERN February 11, 2014. Paper II ATLAS Collaboration. Search for magnetic monopoles and stable particles with high electric charges in 8 TeV pp collisions with the ATLAS detector, Phys. Rev. D, 93, 052009 (2016). Paper III K. Bendtz, D. Milstead, H.-P. H¨achler, A. M. Hirt, P. Mer- mod, P. Michael, T. Sloan, C. Tegner and S. B. Thorarinsson. Search for magnetic monopoles in polar volcanic rocks, Phys. Rev. Lett. 110, 121803 (2014). Reprints were made with permission from the publishers. vii viii Publications not Included in the Thesis As a member of the ATLAS experiment collaboration, I am co-author of 285 publications not referred to in this thesis (April 29 2015). These pa- pers include detector and performance reports as well as physics analyses using ATLAS data. To become an ATLAS author, it is required that you have contributed to the maintenance or development of the ATLAS detec- tor, work which is crucial for the integrity of the research findings of the ATLAS. My contributions concerned studies on the trigger system, which are described in this thesis. In general, ideas, knowledge and frameworks are shared between members of ATLAS, which indirectly makes every project at ATLAS a collaboration between all of its members. ix x Author's Contribution The work contained in this thesis corresponds to four years of research work at the ATLAS experiment at the CERN Large Hadron Collider (LHC), as well as non-ATLAS work. The research has resulted in three papers attached to this thesis. My contributions to Paper I and Paper III were also presented in my licentiate thesis. A large collaboration such as ATLAS releases public results in a vari- ety of ways. In common for each approach, rigorous internal review takes place. Results can be released as papers submitted to journals and as so- called conference notes and public plots. The latter two categories often represent research findings which are updates to earlier journal results and it is considered most efficient to release them in this way. Paper I [1] describes the performance of the ATLAS missing transverse energy triggers and has been subject to internal peer-review of the ATLAS experiment. It is published as a conference note. I contributed to the paper with studies of the MET triggers, concerning both trigger efficiency and distributions of trigger variables. Paper II [2] concerns a search for magnetic monopoles and highly elec- trically charged particles with the ATLAS detector and has been pub- lished in Physical Review D. I produced cut flows for signals and data and participated in evaluating and developing the event selection and the background estimation. I was solely responsible for the statistical proce- dure and for the fiducial regions study where I developed the algorithm for finding the regions. I made large contributions to the event genera- tion and validation, for which I produced both the monopole and HECO single particle samples and the HECO samples with a Drell-Yan-like pro- duction model as well as the Drell-Yan spin-1/2 HECO event generation. This covered event generation, detector simulation, reconstruction and digitisation and production of D3PDs (data format designed for analy- sis). I was responsible for the generation level transverse momentum cuts xi xii Author's Contribution which included making and analysing trigger efficiencies. I contributed to generating samples for the calculation of systematic uncertainties. Paper III [3] describes a search for magnetic monopoles trapped in polar volcanic rocks and has been peer-reviewed by Physics Review Letters. In this search I was responsible for the calibration of the SQUID magne- tometer and for the major part of the data taking. Katarina Bendtz Stockholm, March 2016 Acknowledgments Several sources of energy which more or less systematically have con- tributed positively to the outcome of this thesis have been identified, see Tabs.1-3. I apologize for any group or individual who might have been left out in this section. The lists do not claim to be complete but merely serve as a representative selection of the most dominant contributions. Team/ Person(s) Most Significant Specification Association/ Contribution(s) Relationship supervisor D. Milstead supervision, discussions devoted co-supervisor S. Hellman discussions L1 related office room mates O. Lundberg room atmosphere warm O. Bylund support mental Stockholm ATLAS group PhD students chats lunch-time seniors advise skillful KTH ATLAS PhD students G. Ripellino alliance cordial E. Sidebo acquaintanceship amicable CERN colleague G. Palacino collaboration excellent theorist S. Sj¨ors proof-reading, lecturing QFT HIP analysis group collaboration professional CERN colleague J. Beacham cheer amicable CERN colleague S. Pataraio assistance comitted CERN colleague L. Moneta advise cheerful CERN colleague M. Baak advise statistical predefense comittee J. Edsj¨o comments valuable C. Finley advise professional P.-E. Tegn´er engagement professional ATLAS L1 Calo A. Mincer inspiration professional A. Watson encouragement amicable Table 1: Overview over work related people who have contributed posi- tively to the outcome of this thesis. xiii xiv Acknowledgments Team/ Person(s) Most Significant Specification Association/ Contribution(s) Relationship family F. Bonnevier love, support, food endless family C. Bendtz care, love eternal family C. Bonnevier involvement emotional family C.-G. Ericsson encouragement boundless family T. Bonnevier cheer grandiose family D. Zarins support amiable extended family R. Str¨om inspiration never-ending extended family K., S. and R. Yoshihara friendship faithful extended family A. Isler affection never-ending Table 2: Overview over family members who have contributed positively to the outcome of this thesis. Team/ Person(s) Most Significant Specification Association/ Contribution(s) Relationship friend M. Cegrell support infinite friend L. Johansson friendship considerate friend J. Eriksson frontpage, soul-sharing vital friend A. Ehlde love limitless friend T. Petrushevska devotion perpertual friend J., M. and J. Pearson rendez-vous fantastic friend J. Lundberg affection significant friend M. Tylmad connection spiritual friend A. Sellerholm accord mental friend M. Johanssen affinity intellectual friend J. Ojner¨ care persisting friend A.˚ Hedberg affection continuous friend M. Frankel pact PIA friend J. Cummings understanding mutual friend S. Nohlin connection immaterial friend C. Ohm support IT related friend S. Lee solidarity important friend S. Packal´en discussions intellectual friend M. and S. Eketorp friendship SF initiated friend H. Silvander boost moral